Previous attempts in the prior art to provide apparatus for making ice may be divided into two general groups:
(a) the earlier art which teaches the use of a plurality of spaced apart pipes permanently embedded in material, such as concrete. Water sprayed onto the concrete surface is frozen by having its heat extracted by refrigerated brine flowing through the pipes under pressure. Such systems have disadvantages. e.g. costly repairs in the event a pipe begins to leak and the need for a large volume of brine which has been well documented; PA0 (b) the more recent mats or grids of small diameter plastic tubing which are generally portable from one area to another.
To this second group belongs U.S. Pat. No. 3,751,935 issued to MacCracken et al on Aug. 14, 1973. This patent discloses relatively parallel tubes which are preassembled at the factory with a "securing means S". The latter includes stiffener wire and spacer strips to hold the tubes together in a grid. The main drawbacks of this patent are that the tubes are subject to horizontal and vertical undulations given the loose arrangement of the strips and wire and, therefore, in order to be transported, must be rolled on a reel. The lack of a web joining the tubes requires an auxiliary membrane on porous soils.
Another U.S. patent issued to Remillard on July 26, 1983 and bearing U.S. Pat. No. 4,394,817, also teaches the use of flexible plastic tubing assembled together in "modules". This patent discloses a plurality of parallel tubes in each module joined by an integral horizontal web. The web isolates the half lower portion of each plastic tube from contact with the ice slab Thus,. the total area of heat exchange surface is slightly more than half of the possible maximum value. Another drawback is that the tubes are subject to vertical undulation as in the first-discussed patent. Such undulations cause annoying problems while the ice slab is being built and requires a thicker ice to prevent accidental punctures of tubing by, for example, skaters or an ice resurfacing machine. What is more, in practical applications, it has been found that the modules must often be lifted, so that water can be sprayed thereunder. Such work is time-consuming and toilsome.